Interferometric measuring device

ABSTRACT

The invention relates to an interferometric measuring device ( 1 ) for measuring the shape of a surface of an object (O), with a radiation source (LQ) that emits a short coherence radiation, a beam splitter (ST) for producing an object beam (OS), which is guided along an object light path to the object (O), and a reference beam (RS), which is guided along a reference light path to a reflective reference plane (RSP), and with an image recorder (BA) that records the radiation, which is reflected by the object (O) and the reference plane (RSP) and is brought into interference, and supplies it to an evaluation device to determine the surface shape. A favorable adaptability and operation, even in measuring locations that are difficult to access is achieved by virtue of the fact that a lens system (SO), which is fixed in relation to the object (O), is disposed in the object light path and that the fixed lens system (SO) is followed by a lens system (BO) that can move in the direction of its optical axis.

Prior Art

[0001] The invention is based on an interferometric measuring device formeasuring the shape of a surface of an object, with a radiation sourcethat emits a short coherence radiation, a beam splitter for producing anobject beam, which is guided along an object light path to the object,and a reference beam, which is guided along a reference light path to areflective reference plane, and with an image recorder that records theradiation, which is reflected by the object and the reference plane andis brought into interference, and supplies it to an evaluation device todetermine the surface shape.

[0002] An interferometric measuring device of this kind has beendisclosed by DE 41 08 944 A1. In this known interferometric measuringdevice, which is based on the measuring principle of so-called whitelight interferometry or short coherence interferometry, a radiationsource emits short coherence radiation, which a beam splitter splitsinto an object beam that illuminates a measurement object and areference beam that illuminates a reflective reference plane in the formof a reference mirror. In order to scan the object surface in the depthdirection, the reference mirror is moved in the direction of the opticalaxis of the reference light path by means of a piezoelectric actuatingelement. When the object light path and the reference light pathcoincide, then in the range of the coherence length, there is a maximumof interference contrast, which can be detected by means of aphotoelectric image recorder and a subsequent evaluation device and isevaluated on the basis of the known deflection position of the referencemirror in order to determine the contour of the object surface.

[0003] Other interferometric measuring devices or interferometricmeasuring methods of this kind based on white light interferometry aregiven in “Surface Profiling by Analysis of White-Light Interferograms inthe Spatial Frequency Domain” by P. de Groot and L. Deck, in the Journalof Modern Optics, Vol. 42, No. 2, pp. 389-401, 1995 and in“Endoskopisches 3-D-Formmesssytem” [Endoscopic 3-D Shape-MeasuringSystem] by T. Maack, G. Notni, W. Schreiber, and W.-D. Prenzel, in theJahrbuch für Optik und Feinmechanik [Annual of Optics and FineMechanics], Ed. W.-D. Prenzel, Verlag Schiele und Schoen, Berlin, pp.231-240, 1998.

[0004] With the above-mentioned interferometric measuring devices andmeasuring methods, it is difficult to execute measurements of differentlocations, in particular ones that are difficult to access, e.g. in deepcavities or narrow channels, with a sufficient degree of lateralresolution. In order to eliminate this problem, the (unpublished) GermanPatent Application No. 199 48 813 proposes generating at least oneintermediate image in the arm of the object light path, which achieves agreater lateral resolution even in a narrow cavity or narrow channel. Onthe other hand, enlarging the numerical aperture shortens the depth offocus and also, a scanning of a surface region whose normal (viewingdirection) is oblique to the axis of the image-generating device of theobject light path causes problems in the scanning in the depthdirection.

[0005] The problem of maintaining the depth of focus range in depthscanning can be avoided in that instead of moving the reference plane orthe reference mirror that represents it, the reference light path iskept fixed and the object light path is changed. This can once againtake place in two different ways, i.e. on the one hand, by moving theobject itself in the depth direction or on the other hand, by moving theinterferometric part of the measuring device in relation to the object.These kinds of changes to the object light path as steps taken for depthscanning in white light interferometry are in fact known in and ofthemselves, for example from the above-mentioned journal articles, butare technically difficult to achieve, particularly in the manufacture oftheir parts.

[0006] The object of the invention is to produce an interferometricmeasuring device of the type mentioned at the beginning, which permits asimple adaptability to different measuring problems and whichfacilitates the achievement of the best possible measurement result withthe simplest possible design and the simplest possible measurementexecution.

[0007] This object is attained with the features of claim 1. This claimprovides that a lens system, which is fixed in relation to the object(during measurement), is disposed in the object light path and that thefixed lens system is followed by a lens system that can move in thedirection of its optical axis (during measurement).

[0008] With the fixed lens system and the movable lens system disposedafter it, there are numerous possibilities to simply measure differentsurfaces, even in locations that are difficult to access. For example asurface aligned oblique to the movement direction of the depth scanningcan be scanned in a positionally accurate manner in the depth directionby means of a deflecting element. With different image-generatingelements that deform the wave front, such as refractive, diffractive, orreflective elements (e.g. lenses, concave mirrors, gratings, etc.) or acombination of optical elements of this kind, there are a varietypossibilities for adapting to a respective measurement problem withoutrequiring a costly modification to the overall design of the measuringdevice.

[0009] If the fixed lens system is entirely or partially embodied as anendoscope, then it is possible to achieve a relatively high lateralresolution even when measuring in narrow cavities.

[0010] If the fixed lens system is part of a lens system that generatesan intermediate image, then the cost of adapting the measuring device todifferent measuring tasks is reduced considerably further. In thisconnection, it is particularly good if the intermediate image of thelens system generating in the intermediate image is disposed in theobject light path.

[0011] In order to achieve a measurement that stands up to lateralrelative motion of the object, the invention advantageously providesthat the fixed lens system generates an image of the object towardinfinity.

[0012] A variety of designs are comprised in that the movable lenssystem is disposed entirely outside, partially inside and outside, orentirely inside the object light path.

[0013] The measure of comprising the movable lens system entirely orpartially of optic elements, which can move in the optical axis, caneasily be used to produce a zoom lens, for example.

[0014] The precision of the measurement is increased by the step ofplacing an image of the reference plane in the depth of focus range ofthe lens system that generates the image of the object on the imagerecorder (image-generating lens system). In this connection, the imageof the reference plane is advantageously placed in the image plane ofthe image-generating lens system and in addition, the image of thereference plane moves synchronously with the image plane of theimage-generating lens system when the movable lens system moves.

[0015] An advantageous embodiment of the invention is also comprised inthat the fixed lens system is embodied as a fixed intermediateimage-generating device, with which at least one intermediate image ofthe object surface—preferably in the object light path—is generated,which is fixed in relation to the object, and that the movable lenssystem is embodied as an objective lens system, which is disposed behindthe fixed intermediate image in the beam path and can move in thedirection of its optical axis in order to scan the fixed intermediateimage, which is aligned normal to this axis, in the depth direction andto generate an image of it on the image recorder directly or by means ofone or more intermediate images. Generating the fixed intermediate imageof the object surface, which is disposed for example in the object lightpath, by means of the fixed intermediate image-generating device in theobject light path on the one hand makes it possible, even in narrowchannels or bores, to detect the object surface to be measured with arelatively high degree of lateral resolution and makes it possible toevaluate it with regard to the depth structure through the use of theimage recorder and the subsequent evaluation device. The scanning of thefixed intermediate image can be executed with relatively simple stepssince only a few optical components of the object light path have to bemoved to scan its depth; the scanned depth of the fixed intermediateimage always remains in the depth of focus range of the movableobjective lens system since by means of the depth scan, the object planeof the movable objective lens system is moved, so to speak, through thefixed intermediate image and in this manner, the interference maxima inthe range of the greatest focus are evaluated. Furthermore, the fixedintermediate image is always aligned or can always be aligned normal tothe movement direction of the objective lens system since even when theobject surface being considered is disposed oblique relative to the axisof the object light path, an image of it can easily be generated normalto the axis of the moving objective lens system. This permits an easymeasurement of surface regions whose normals are aligned oblique to themovement direction of the objective lens system.

[0016] The image generation quality and precision of the evaluation areimproved by virtue of the fact that the intermediate image-generatingdevice has the same image-generating scale for all of the object pointsthat appear in the intermediate image. For example, the design can beembodied in such a way that the intermediate imagegenerating device isembodied as a telecentric image-generating device in a 4f apparatus.

[0017] In order to achieve more precise measuring results, it is alsoadvantageous that a lens system, which at least partially corresponds to(or is identical to) the lens system in the object light path, isprovided in the reference light path for compensation.

[0018] An advantageous embodiment of the measuring device for executinga large-area evaluation of the surface region being considered iscomprised in that the image recorder has image recording elements(pixels) disposed over a large area and that for each pixel, theposition of the objective lens system at which the greatest interferencecontrast occurs is detected.

[0019] The depth scanning of an obliquely disposed object surface iseasily permitted by virtue of the fact that when a viewing direction ofthe intermediate image-generating device diverges from the normal of theobject surface, an image-generating unit is provided for generating theintermediate image.

[0020] A simple, easy-to-use design of the measuring device is improvedby virtue of the fact that a movable unit includes an illumination unitwith the light source and the beam splitter in addition to the movableobjective lens system or includes only the beam splitter in addition tothe movable objective lens system.

[0021] An embodiment of the measuring device that is favorable from bothan operational and a design standpoint is also comprised in that thefixed intermediate image-generating device is embodied as an endoscope.

[0022] The measure of providing a set of fiber optics to illuminate theobject and the reference plane achieves the advantage that reflectionsagainst the lenses of the image-generating device are reduced.

[0023] Various possible embodiments of the light paths are achieved byvirtue of the fact that the lenses of the object light path, thereference light path, and other light paths are achromatic lenses, grinlenses (gradient index lenses), or rod-shaped lenses.

[0024] The shape measurement is improved by virtue of the fact that anoptical element is disposed in the image-generating lens system, insideor outside the object light path, which permits the image to be rotatedinto a position that is favorable for the evaluation.

[0025] Access to a measuring location inside an object can befacilitated by virtue of the fact that a tilting endoscope, as the fixedlens system or part of the fixed lens system, is disposed in the objectlight path and can be moved into at least two tilt positions with anangle between the untilted and tilted positions.

[0026] The invention advantageously provides that the tilting endoscopehas two tubes, which are connected to each other by means of a joint andwhich contain optical components of the tilting endoscope including adeflecting element.

[0027] The tilt positions can be easily set by virtue of the fact that aspring mechanism is provided in the vicinity of the joint and cooperateswith the two tubes.

[0028] The invention will be explained in detail below in conjunctionwith exemplary embodiments with reference to the drawings.

[0029]FIGS. 1A and 1B show schematic depictions of a first exemplaryembodiment of an interferometric measuring device, with a deflectingunit that is fixed in relation to an object, in two different depthscanning positions,

[0030]FIGS. 2A and 2B show depictions of another exemplary embodiment ofthe interferometric measuring device, where the deflecting element isreplaced by image-generating elements that deform the wave front, in twodifferent scanning positions,

[0031]FIG. 3 shows another exemplary embodiment of the interferometricmeasuring device, with a different arrangement of the optically fixedelements in the object light path,

[0032]FIGS. 4A and 4B show another exemplary embodiment of theinterferometric measuring device in which the size of a movable unit ofthe reference light path is shown in a reduced scale,

[0033]FIGS. 5A and 5B show another exemplary embodiment in which boththe movable lens system and the reference mirror are moved,

[0034]FIG. 6 is a schematic depiction of another exemplary embodiment ofan interferometric measuring device,

[0035]FIG. 7 shows the interferometric measuring device according toFIG. 6, with a device for measuring an oblique object surface,

[0036]FIG. 8 shows another example of the interferometric measuringdevice in which the number of moving elements is reduced in comparisonto FIGS. 6 and 7,

[0037]FIG. 9 shows another exemplary embodiment of the interferometricmeasuring device in which the number of moving elements is furtherreduced,

[0038]FIG. 10 shows another embodiment of the interferometric measuringdevice in which a fiber optic device is provided for illumination,

[0039]FIG. 11 shows another embodiment of the interferometric measuringdevice, with a device for rotating the image,

[0040]FIG. 12 shows an embodiment of the interferometric measuringdevice with a tilting endoscope, during an insertion procedure,

[0041]FIG. 13 shows the measuring device according to FIG. 12 in themeasuring position, and

[0042]FIGS. 14a) to c) show different depictions of the tiltingendoscope.

[0043] In an interferometric measuring device 1 shown in FIGS. 1A and1B, short coherence radiation of a radiation source or light source LQ(e.g. a light-emitting diode or superluminescence diode) whose coherencelength is typically on an order of magnitude of approx. 10 μm (e.g. 3 to100 μm) is conveyed via a lens L4 and other optical elements to a beamsplitter ST and is split in this beam splitter ST into an object beamOS, which is guided to a surface of an object O, and a reference beamRS, which is guided to a reference mirror RSP.

[0044] In the object light path or object arm, a fixed lens system SO inthe form of a reflective deflecting unit AE is disposed in front of theobject O so that the obliquely positioned object O is always scannedperpendicular to its surface in the depth direction, as shown in FIGS.1A and 1B, in which two different scanning depths are shown, which areproduced by deflecting a moving unit BEW by means of a movementgenerator BE attached to it, for example a piezoelectric element. Avirtual reference plane VR is therefore situated in the normal directionat various depths in relation to the object O. The fixed lens system SO,which in this instance is constituted by the deflecting unit AE, isfixed in relation to the object O. It is followed in the beam path by amovable lens system BO, which is disposed in the moving unit BEW, in thebeam path between the beam splitter ST and the image recorder A.

[0045] During the depth scanning, if the object light path and thereference light path coincide due to the movement of the moving unitBEW, then a maximum of the interference contrast is produced in therange of the coherence length, which interference contrast is detectedby means of the photoelectric image recorder BA and a subsequentevaluation device and is evaluated based on the known deflectionposition in order to determine the contour of the object surface.

[0046] In the additional exemplary embodiment shown in FIGS. 2A and 2B,in which two different deflection positions of the moving unit BEWproduced by the movement generator BE are shown, in comparison to theprevious exemplary embodiment, the fixed lens system SO is embodieddifferently, namely by means of image-generating elements in the form oflenses L2, L3 that deform the wave front. The fixed lens system SOgenerates a fixed intermediate image in an intermediate image plane ZE,which is scanned in the depth direction by means of the movable lenssystem disposed in the moving unit BEW. This measure makes it possibleto simply adapt essentially the same scanning unit to differentmeasuring situations; for example, a measurement with a relatively highdegree of lateral resolution in narrow cavities is achieved. There isalso no trouble with regard to depth of focus since the object surfaceis always optimally aligned in relation to the image-generating movablelens system BO. By means of the image-generating lens system, whichcontains the fixed lens system SO and the movable lens system BO, animage of the object O is generated on the image recorder BA. Through theappropriate arrangement of the components in the moving unit BEW, it ispossible to move the image of the reference plane VR along with theimage plane of the image-generating lens system.

[0047] In another exemplary embodiment shown in FIG. 3, the fixed lenssystem SO includes an image-generating element, which changes the wavefront and is in the form of the lens L3, and a deflecting unit in theform of a refracting element so that once again, an object surfacedisposed oblique in relation to the depth scanning direction is alwaysmeasured in a positionally accurate manner. In this case, however,another element, which changes the wave front and is in the form of thelens L2, is disposed inside the moving unit BEW so that this embodimentdoes in fact also permit a simple adaptation in a scanning device, buton the other hand, the depth measurement range is limited to the depthof focus since the whole image plane does not move along with the depthscanning. The fixed lens system SO generates an image of the objecttoward infinity.

[0048] In the exemplary embodiment that is likewise shown in twodifferent scanning positions in FIGS. 4A and 4B, the moving unit BEW isembodied so that it is very small; a greater diameter ofimage-generating lenses in the reference light path is used inconnection with the beam distribution in the beam splitter ST.

[0049] In another exemplary embodiment shown in FIGS. 5A and 5B, amoving unit BEW is respectively provided in the reference light path andin the object light path, and is synchronously deflected by means of arespectively associated movement generator BE.

[0050] Other preferred exemplary embodiments are shown in FIGS. 6 to 10.In the exemplary embodiment according to FIG. 6, an intermediateimage-generating device SO (also referred to below as the bayonet lenssystem) with intermediate image-generating lenses L2, L3, which is fixedin relation to the object O, is disposed as a fixed lens system SO inthe object light path or object arm and generates a fixed intermediateimage SZB of the object surface. The reference light path corresponds inlength to the object light path so that a virtual reference VR issituated in the vicinity of the object surface. An image of the virtualreference VR is generated by the bayonet lens system SO as an image ofthe reference plane BR in the vicinity of the fixed intermediate imageSZB. For a favorable design and operation, the bayonet lens system SO isembodied like an endoscope and is attached, for example, to a housingthat contains the rest of the optical system. In another possibleembodiment, the bayonet lens system SO is mechanically separate from thehousing and is coupled to the object O in a stationary fashion.

[0051] The reference light path or reference arm contains opticalelements, which essentially correspond to the optical elements of theobject arm and are embodied in the form of a compensated lens system KSOso that interfering optical properties of the lens system in the objectlight path are compensated.

[0052] The fixed intermediate image SZB generated by the bayonet lenssystem SO is scanned in the depth direction, i.e. parallel to itsnormal, by means of the lens system BO, which can be moved parallel tothe normal direction, i.e. along its optical axis (depth scanning). Theimage of the reference plane BR is situated in the depth of focus rangeof the movable objective, preferably in the object plane of the movableobjective or the movable objective lens system. The depth scanning takesplace by virtue of the fact that the movable objective lens system BO ismoved relative to the fixed intermediate image SZB, which assures thatthe image of the reference plane BR moves synchronously along with themovable objective lens system BO.

[0053] As a result, during the scanning of the movable objective BO, theimage of the reference plane BR is moved through the fixed intermediateimage SZB.

[0054] The fixed intermediate image SZB is projected by the movableobjective lens system BO directly or by means of at least oneintermediate image generation step onto an image recorder BA , which hasa multitude of image recording elements disposed next one another, e.g.a CCD camera, and is evaluated in a subsequent evaluation device inorder to determine the surface shape, e.g. through detection of themaxima of the interference contrast, which forms the basis for therespective position of the movable objective BO.

[0055] In the image of the object on the image recorder BA, there is ahigher interference contrast if a path difference between the object armand the reference arm is less than the coherence length. Differentintrinsically known methods can be used to obtain a 3-D vertical profile(see the references cited at the beginning).

[0056] For example, the design shown in FIG. 6 and also in thesubsequent figures contains a Michelson interferometer. It is alsopossible to generate a number of intermediate images with the fixedbayonet lens system SO. The shaded region is moved for the scanning;this shaded region can be contained inside a housing, for example,against which in bayonet lens system SO is placed. Alternatively, thebayonet lens system SO can also be separate from the housing and can beconnected to the object in a stationary fashion.

[0057] In the design shown in FIG. 7, the surface of the object O to bemeasured is disposed oblique relative to the optical axis of the bayonetlens system SO and a deflecting element AE or a differentimage-generating unit is positioned in front of the object, whichelement generates a fixed intermediate image SZB that is alignednormally in relation to the optical axis of the movable objective BO.The scanning of the fixed intermediate image SZB permits the scanning ofthe oblique object surface to be executed by means of simple measuressince the viewing direction of the optical axis of the movable objectiveBO is aligned at 0° in relation to the intermediate image. Then thescanning axis need only be aligned parallel to the axis of the movableobjective BO. The viewing direction of the bayonet lens system SO istherefore independent of the scanning axis of the depth scanning.

[0058] In the design of the interferometric measuring device 1 shown inFIG. 8, the number of moving components that execute the depth scanningis significantly reduced, as indicated by the number of elementsdepicted in the shaded region, which essentially includes the referencearm, the beam splitter ST, and the movable objective BO.

[0059] Another exemplary embodiment for the interferometric measuringdevice 1 with a scanning of the fixed intermediate image SZB is shown inFIG. 9. In this instance, in addition to the movable objective BO, thebeam splitter ST and the illumination unit with the light source LQ aremoved. A slight shifting of the reference beam lateral to the opticalaxis of the reference arm has practically no effect on the measuringresult due to the relatively slight scanning movement distance.

[0060] In the exemplary embodiment shown in FIG. 10, the object O isalternatively illuminated by means of a fiber optic light guide LL,which extends at least partially inside the bayonet lens system SO. Thisfiber optic illumination has the advantage of reducing reflectionsagainst the lenses of the bayonet lens system SO. In order to balancethe optical path lengths and dispersion in the object arm and thereference arm, the fiber lengths and geometries in the twointerferometer arms should be selected so as to correspond with eachother to the greatest degree possible.

[0061] A variety of embodiments can be selected for the lenses containedin the interferometric measuring device, e.g. achromatic lenses, grinlenses (gradient index lenses), or rod-shaped lenses.

[0062] In the exemplary embodiment shown in FIG. 11, theimage-generating lens system contains an optical element DE for rotatingthe image. If the fixed lens system SO is rotated in relation to theobject, e.g. in order to measure different segments of a radiallysymmetrical object (e.g. a valve seat), then the image of the object Oalso rotates on the image recorder BA. However, it is advantageous tohave a fixed image of the object on the image recorder BA. This can beachieved in that an optical element (e.g. a reversion prism, dove prism,etc.), which can compensate for the rotation of the image, is providedin the image-generating lens system, preferably outside the object lightpath.

[0063] FIGS. 12 to 14 show another exemplary embodiment of theinterferometric measuring device in which the fixed lens system SO isembodied as a tilting endoscope KL.

[0064] The tilting endoscope KL is comprised, for example, of two tubesT1, T2, which have respective tube axes TA1, TA2 and are connected toeach other with a joint G in order to form a tilting axis KA of the onetube T1 in relation to the other tube T2. For example, the two tubes T1,T2 can assume two different tilt positions, which differ by a tiltingangle α, as can be seen in FIGS. 14b) and c). In the current instance,the two tubes T1, T2 are mechanically produced so that in the untiltedposition, the two tube axes TA1, TA2 form an angle of 0°, whereas in thetilted position, they are oriented at the predetermined tilting angle αin relation to each other. Between the tubes T1, T2, which contain theoptical components OKL of the tilting endoscope, a spring mechanism witha spring F is provided in the vicinity of the joint G. If the tiltingendoscope KL is in the untilted position, then the spring F is understress, whereas in the tilted position, the spring is unstressed. In thecurrent instance, the endoscope lens system is designed for the tiltedposition. The endoscope lens system contains at least one opticaldeflecting element, e.g. a mirror KSP, which is disposed in the vicinityof the joint G. Prisms or gratings can also be conceivably used asdeflecting elements, through which the optical axis is deflected inaccordance with the tube axes TA1, TA2. As shown in FIG. 12, wheninserted into the object O, the tilting endoscope KL is in the untiltedposition. If the spring is under stress, this insertion can be achievedby virtue of the endoscope having its own guide mechanism. However, theobject itself can also serve as a guide mechanism, e.g. a guide bore ina valve seat measurement as shown in FIGS. 12 and 13. If the tiltingendoscope KL is inserted completely into the object O or the component,then the joint G should be unconfined so that the tilting endoscope KLcan assume the tilted position. The tilting endoscope KL is manufacturedso that in the tilted position, it observes the measuring location MSTprecisely.

[0065] In the tilted position, the object surface to be observed isilluminated with a plane wave by the tilting endoscope KL and an imageof it is generated directly or by means of an intermediate image on theimage recorder BA (e.g. CCD camera). In the reference light path, thereference beam RS is reflected by the reference mirror RSP. In order tocompensate the endoscope lens system, a lens system that is similar orcorresponds to the endoscope lens system can also be placed here in thereference light path or reference arm. The data evaluation takes placeas described in connection with the preceding exemplary embodiments.

[0066] The interferometer here can also be embodied other than as aMichelson interferometer (e.g. as a common path interferometer, aMach-Zehnder interferometer, etc.).

1. An interferometric measuring device (1) for measuring the shape of asurface of an object (O), with a radiation source (LQ) that emits ashort coherence radiation, a beam splitter (ST) for producing an objectbeam (OS), which is guided along an object light path to the object (O),and a reference beam (RS), which is guided along a reference light pathto a reflective reference plane (RSP), and with an image recorder (BA)that records the radiation, which is reflected by the object (O) and thereference plane (RSP) and is brought into interference, and supplies itto an evaluation device to determine the surface shape, characterized inthat a lens system (SO), which is fixed in relation to the object (O),is disposed in the object light path and that the fixed lens system (SO)is followed by a lens system (BO) that can move in the direction of itsoptical axis.
 2. The measuring device according to claim 1,characterized in that the fixed lens system (SO) has elements thatdeform the wave front.
 3. The measuring device according to claim 1 or2, characterized in that the fixed lens system (SO) is entirely orpartially embodied as an endoscope.
 4. The measuring device according toone of the preceding claims, characterized in that the fixed lens system(SO) is part of a lens system that generates an intermediate image. 5.The measuring device according to one of the preceding claims,characterized in that the fixed lens system (SO) generates an image ofthe object toward infinity.
 6. The measuring device according to one ofthe preceding claims, characterized in that the movable lens system (BO)is disposed entirely outside, partially inside and outside, or entirelyinside the object light path.
 7. The measuring device according to oneof the preceding claims, characterized in that the movable lens system(BO) is comprised entirely or partially of optical elements that aresupported so that they can move in the optical axis.
 8. The measuringdevice according to one of the preceding claims, characterized in thatan image of the reference plane (VR) is situated in the depth of focusrange of the image-generating lens system.
 9. The measuring deviceaccording to claim 8, characterized in that the image of the referenceplane (VR) is situated in the image plane of the image-generating lenssystem.
 10. The measuring device according to claim 8 or 9,characterized in that the image of the reference plane (VR) movessynchronously with the image plane of the image-generating lens systemwhen the movable lens system (BO) is moved.
 11. The measuring deviceaccording to one of the preceding claims, characterized in that thefixed lens system (SO) is embodied as a fixed intermediateimage-generating device (L2, L3), with which at least one intermediateimage (SZB) of the object surface is generated, which is fixed inrelation to the object (O), and that the movable lens system (BO) isembodied as an objective lens system, which is disposed behind the fixedintermediate image (SZB) in the beam path and can move in the directionof its optical axis (ROA) in order to scan the fixed intermediate image(SZB), which is aligned normal to this axis, in the depth direction (Z)and to generate an image of it on the image recorder (BA) directly or bymeans of one or more intermediate image-generating steps.
 12. Themeasuring device according to claim 11, characterized in that theintermediate image-generating device (L2, L3) has the sameimage-generating scale for all of the object points that appear in theintermediate image (SZB).
 13. The measuring device according to claim12, characterized in that the intermediate image-generating device (L2,L3) is embodied as a telecentric image-generating device in a 4fapparatus.
 14. The measuring device according to one of the precedingclaims, characterized in that a lens system (KSO), which at leastpartially corresponds to the lens system in the object light path, isprovided in the reference light path for compensation.
 15. The measuringdevice according to one of the preceding claims, characterized in thatthe image recorder (BA) has image recording elements (pixels) disposedover a large area and that for each pixel, the position of the objectivelens system (BO) at which the greatest interference contrast occurs isdetected.
 16. The measuring device according to one of the precedingclaims, characterized in that when a viewing direction of theintermediate image-generating device (L2, L3) diverges from the normalof the object surface, a deflecting element (AE) is provided forgenerating the intermediate image (SZB).
 17. The measuring deviceaccording to one of the preceding claims, characterized in that amovable unit includes an illumination unit with the light source (L2)and the beam splitter (ST) in addition to the movable objective lenssystem (BO) or includes only the beam splitter (ST) in addition to themovable objective lens system (BO).
 18. The measuring device accordingto one of claims 11 to 17, characterized in that the fixed intermediateimage-generating device (L2, L3) is embodied as an endoscope.
 19. Themeasuring device according to one of the preceding claims, characterizedin that a set of fiber optics (LL) are provided to illuminate the object(O) and the reference plane (RSP).
 20. The measuring device according toone of the preceding claims, characterized in that the lenses (L1, L2,L3, L4, KSO) of the object light path, the reference light path, andother light paths, are individual lenses, grin lenses (gradient indexlenses), rod-shaped lenses, diffractive elements, prisms, orcombinations thereof.
 21. The measuring device according to one of thepreceding claims, characterized in that an optical element (DE) isdisposed in the image-generating lens system, inside or outside theobject light path, which permits the image to be rotated into a positionthat is favorable for the evaluation.
 22. The measuring device accordingto one of the preceding claims, characterized in that a tiltingendoscope (KL), as the fixed lens system (SO) or part of the fixed lenssystem (SO), is disposed in the object light path and can be moved intoat least two tilt positions with an angle (α) between the untilted andtilted positions.
 23. The measuring device according to claim 22,characterized in that the tilting endoscope (KL) has two tubes (T1, T2),which are connected to each other by means of a joint (G) and whichcontain optical components (OKL) of the tilting endoscope (KL) includinga deflecting element (KSP).
 24. The measuring device according to claim23, characterized in that a spring mechanism (F) is provided in thevicinity of the joint (G) and cooperates with the two tubes (T1, T2).